Mars Express finds evidence for large aquifers on early Mars(Forwarded)

ESA News
http://www.esa.int

30 November 2005

Mars Express evidence for large aquifers on early Mars

Substantial quantities of liquid water must have been stably present in
the early history of Mars. The findings of OMEGA, on board ESA's Mars
Express, have implications on the climatic history of the planet and the
question of its 'habitability' at some point in its history.

These conclusions were drawn thanks to data on Martian surface minerals
obtained by OMEGA (Observatoire pour la Mineralogy, l'Eau, les Glaces et
l'Activité), the visible and infrared mapping spectrometer on board ESA's
Mars Express.

From previous observations, Mars must have undergone water-driven
processes, which left their signature in surface structures such as
channel systems and signs of extensive aqueous erosion. However, such
observations do not necessarily imply the stable presence of liquid water
on the surface over extended periods of time during the Martian history.

The data collected by OMEGA unambiguously reveal the presence of specific
surface minerals which imply the long-term presence of large amounts of
liquid water on the planet.

These 'hydrated' minerals, so called because they contain water in their
crystalline structure, provide a clear 'mineralogical' record of
water-related processes on Mars.

During 18 months of observations OMEGA has mapped almost the entire
surface of the planet, generally at a resolution between one and five
kilometres, with some areas at sub-kilometre resolution.

The instrument detected the presence of two different classes of hydrated
minerals, 'phyllosilicates' and 'hydrated sulphates', over isolated but
large areas on the surface.

Both minerals are the result of a chemical alteration of rocks. However,
their formation processes are very different and point to periods of
different environmental conditions in the history of the planet.

Phyllosilicates, so-called because of their characteristic structure in
thin layers ('phyllo' = thin layer), are the alteration products of
igneous minerals (minerals of magmatic origin) sustaining a long-term
contact with water. An example of phyllosilicate is clay.

Phyllosilicates were detected by OMEGA mainly in the Arabia Terra, Terra
Meridiani, Syrtis Major, Nili Fossae and Mawrth Vallis regions, in the
form of dark deposits or eroded outcrops.

Hydrated sulphates, the second major class of hydrated minerals detected
by OMEGA, are also minerals of aqueous origin. Unlike phyllosilicates,
which form by an alteration of igneous rocks, hydrated sulphates are
formed as deposits from salted water; most sulphates need an acid water
environment to form. They were spotted in layered deposits in Valles
Marineris, extended exposed deposits in Terra Meridiani, and within dark
dunes in the northern polar cap.

When did the chemical alteration of the surface that led to the formation
of hydrated minerals occur? At what point of Mars's history was water
standing in large quantities on the surface? OMEGA's scientists combined
their data with those from other instruments and suggest a likely scenario
of what may have happened.

"The clay-rich, phyllosilicate deposits we have detected were formed by
alteration of surface materials in the very earliest times of Mars," says
Jean-Pierre Bibring, OMEGA Principal Investigator.

"The altered material must have been buried by subsequent lava flows we
observe around the spotted areas. Then, the material would have been
exposed by erosion in specific locations or excavated from an altered
crust by meteoritic impacts," Bibring adds.

Analysis of the surrounding geological context, combined with the existing
crater counting techniques to calculate the relative age of surface
features on Mars, places the formation of phyllosilicates in the early
Noachian era, during the intense cratering period. The Noachian era,
lasting from the planet's birth to about 3.8 thousand million years ago,
is the first and most ancient of the three geological eras on Mars.

"An early active hydrological system must have been present on Mars to
account for the large amount of clays, or phyllosilicates in general, that
OMEGA has observed," says Bibring.

The long-term contact with liquid water that led to the phyllosilicate
formation could have existed and be stable at the surface of Mars, if the
climate was warm enough. Alternatively, the whole formation process could
have occurred through the action of water in a warm, thin crust.

OMEGA data also show that the sulphate deposits are distinct from, and
have been formed after, the phyllosilicate ones. To form, sulphates do not
need a particularly long-term presence of liquid water, but water must be
there and it must be acidic.

The detection and mapping of these two different kinds of hydrated
minerals point to two major climatic episodes in the history of Mars: an
early -- Noachian -- moist environment in which phyllosilicates formed,
followed by a more acid environment in which the sulphates formed. These
two episodes were separated by a Mars global climatic change.

"If we look at today's evidence, the era in which Mars could have been
habitable and sustained life would be the early Noachian, traced by the
phyllosilicates, rather than the sulphates. The clay minerals we have
mapped could still retain traces of a possible biochemical development on
Mars," Bibring concludes.

Note to editors:

These results appear on line in Nature, on 30 November 2005, in an article
called: 'Phyllosilicate on Mars and implications for early Martian
climate', by:

F. Poulet, J-P. Bibring, Y. Langevin, B. Gondet and C. Gomez (Institut
d'Astrophyisique Spatiale, Univ. of Paris Sud and CNRS, Orsay, France);
J.F. Mustard and A. Gendrin (Geological Sciences, Brown Univ., Rhode
Island, USA); N. Mangold (Interactions & Dynamique des Environment de
Surface, Orsay, France); R.E. Arvidson (Earth & Planetary Sciences,
Washington Univ., St. Louis, USA); and the OMEGA team.

For more information:

Jean-Pierre Bibring, OMEGA Principal Investigator
Institut d'Astrophyisique Spatiale, University Paris Sud and CNRS, Orsay,
France
E-mail: jean-pierre.bibring @ ias.u-psud.fr

Agustin Chicarro, ESA Mars Express Project Scientist
E-mail: agustin.chicarro @ esa.int

Fred Jansen, ESA Mars Express Mission Manager
E-mail: fjansen @ rssd.esa.int

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Related links

* Mars Express instruments
http://www.esa.int/SPECIALS/Mars_Exp...C75V9ED_0.html
* Huygens instruments
http://www.esa.int/SPECIALS/Cassini-...W82VQUD_0.html
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[NOTE: Images supporting this release are available at
http://www.esa.int/SPECIALS/Results_...1UULWFE_1.html
]